Model
8901B
Operation
conditions.) The
-1
block in the supervisor is where the hardware state
is
made to conform
with the software state.
The hardware state
is
the actual, current
state
of the internal settings of the instrument and is only
updated when enough time is allowed between commands
for
the Software Supervisor measurement
loop
to
be completed successfully without interruption; e.g., when
a
trigger is received.
blocks manipulate hardware
as
well and also
measurement.
A
measurement
is
not made
until all blocks are successfully completed in succession. If a block is not completed, a negative
decision
after
that block then forces the program back
to
the top of the supervisor,
measurement for that loop.
In a normal, stable measurement cycle, the program takes the
lhneasurement Display1
branch at the top
block. However,
exists, the
jNon-Measurement Display1
branch will be traversed. This will light an appropriate display, which
is
usually
‘‘-
- -
-
”,
and send the program back through the
1-1
block.
of
the supervisor and
so
avoids the extra time associated with the
if
the program loops back before taking a measurement,
or
if
After
power-up, the external system controller can be thought of
as
a medium through which the user
requests a certain instrument setup which
is
first
implemented in software state and then in hardware
state. Controller commands
(
IKeyboard or HP-IB Interrupts1
)
are treated
as
non-returnable interrupts and
break the flow around the Software Supervisor loop, forcing the internal microprocessor
to
execute
a short program
to
change the software state and then return
to
the loop as shown in the diagram.
The commands applicable to the measurement mode are implemented in software
state
and then
in
hardware state at the next
1-1.
NOTE
Controller routines modify only the software state and do not affect the
hardware immediately.
Since a
]Keyboard or HP-IB Interrupti
can interrupt the Supervisor at any point
and return it
to
the point in the loop before
-1,
these interrupts
abort the current measurement and start a new measurement cycle.
The actual instrument setup
is
guaranteed to conform to the Keyboard
request only at the moment
a
measurement is taken
(
PI).
3-35
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